1. Field of the Invention
The present invention relates generally to a track following servo arrangement for a disk drive unit, and more particularly to a transducer head skew arrangement used in a rigid multiple disk drive data storage system for improving track-to-track seek times.
2. Description of the Prior Art
Computers often include auxiliary memory storage units having media on which data can be written and from which data can be read for later use. Disk drive units incorporating stacked, commonly rotated rigid magnetic disks are used for storage of data in magnetic form on the disk surfaces. Transducer heads driven in a path toward and away from the drive axis write data to the disks and read data from the disks. The data is recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks.
Data located on a particular track on a disk surface is read or written by properly positioning a data transducer head directly over the track. In order to maintain the head in proper position over the data track, track following servo systems often are incorporated into disk drives. Servo position control is used to position the data heads in registration with the data information tracks. One servo system uses a dedicated transducer head to read position signals recorded in servo information tracks on a dedicated disk surface. The data heads are ganged with the servo head for simultaneous movement relative to the data information tracks and the servo information tracks. To access the disk drive unit, a feedback controlled drive system locates the servo head in a desired position, thereby to locate a data head in registration with a specific data information track where data is to be written or read.
For example, U.S. Pat. No. 3,838,457 discloses a track following system detecting special servo signals written on a dedicated servo disk surface by a dedicated servo transducer head. The disclosed system distinguishes one track from another within a repeating group of tracks. A biasing signal is added to the detected signal when the transducing head is located more than one-half track from the target track. A position error signal is produced having a linear slope over the group number of tracks for enabling electrically offsetting of the transducing head up to one-half the group number of tracks by modifying the position error signal.
U.S. Pat. No. 4,807,063 discloses a head position control system for a disk storage unit using a data-surface-servo system with reference information written only into one portion of each track of data in the circumferential direction. The reference information storage regions are arranged on each major surface of each disk with an angular spacing of 360.degree./4N (where N is the number of disks). The reference information storage regions for the respective disks are equiangularly displaced from each other, so that the reference information is read out from the angularly displaced reference information storage regions during each rotation of the disk to detect a displacement of the head from its normal or proper position every time the reference information is read out, and the displacement of the head is corrected in accordance with the detected displacement.
U.S. Pat. No. 4,809,120 discloses a head position control system using reference information regions on the disk surfaces mutually displaced for respective disks. During rotation of the disks, reference information is read out from the regions mutually displaced on the surfaces of the multiple disks. A deviation of each head from a normal or proper head position in relation to a specific track is detected so that in response to the detected deviation, a position of each head is corrected.
Japanese patent No. 58-1812 discloses an initializing system for a mobile head type magnetic device to eliminate the waiting time when a data process jumps over a cylinder, by setting the head record of the contiguous cylinder at a position angularly shifted, or jumped, by an extent equivalent to the seek time of the magnetic head.
Japanese patent application No. 25-8969/89 filed Oct. 5, 1989 discloses a disk apparatus having q heads and q disk surfaces where q is not less than 2. The disk surfaces include the same number of sectors and each disk surface includes a servo sector. Servo information for head positioning is recorded in each servo sector. Servo information is successively read out from the q disk surfaces. Successive q servo informations are averaged to control a position or a speed of the head for the disk surface from which the last servo information is read out.
For any servo control arrangement to be used in a disk drive unit, it is important to minimize the time required to move the data head transducer from a present track to a specified track position. Often the track-to-track seek time or the time needed to move from one track to an adjacent track is the most important factor in the overall file data transfer rate.